Once S is in the atmosphere, it can travel many kilometers from 

 the source and affect forests and cropland. A study of soil and vege- 

 tation around a high-S , Fe-sintering plant in Ontario showed that 



2 2 



birch trees were totally killed on 108 km , heavily killed on 191 km , 



2 

 and damaged on 589 km downwind from the plant. Damage occurred up to 



48 km from the plant in the direction of the prevailing air currents 



(Rao and Leblanc, 1967; McGovern and Balsillie, 1974). 



1.2.1.2 Damage to animals 



The levels of SO in the atmosphere which may be harmful to higher 

 animals and humans are greater than that which may be harmful to 

 plants. Levels greater than 1 ppm were necessary before significant 

 airway resistance occurred in healthy male adults exposed for 10 to 30 

 minutes (Frank et al., 1962). Other cases of the effects of S0„ and 

 H SO, in the atmosphere on human health are reviewed by Schlenker and 

 Jaeger (1980) . 

 1.2.2 Sources of Atmospheric Sulfur 



Sulfur can exist in the atmosphere as S0„, H SO,, particulate sul- 

 fates, H„S , and methylmercaptan (CH SH) (Terman, 1978; Urone and 

 Kenny, 1980). Sulfur dioxide constitutes about 95% of the S compounds 

 produced by the combustion of S-containing fossil fuels (Kellogg et 

 al., 1972). Hydrogen sulfide, the primary S-containing product of 

 anaerobic decomposition of organic matter, is rapidly oxidized to S0 9 

 and S0„ in the atmosphere. 



When SO, dissolves in a cloud or fog droplets or is adsorbed on 

 particle surfaces, it reacts with water to form H ? S0- which is rapidly 

 oxidized by dissolved oxygen or ozone to H„S0, . The detailed mechanism 



